The present invention relates to a device used to break up blood clots or thrombi which form within arteries. In particular, the device is particularly well adapted to break up such clots or thrombi which may form within a coronary artery.
Approximately 1.2 million Americans suffer heart attacks each year. A large percentage of the heart attacks are caused by blood clots or thrombi which form within the coronary arteries. A thrombus is nature's way of stemming the loss of blood from its pipeline system by corking off an opening into the vascular tree. The biochemical process which results in thrombus formation is not fully understood. However, in simple terms, injury to the vascular wall releases chemicals which lead to conversion of soluble circulating fibrinogen molecules into a polymeric structure of fibrin. The fibrin structure is insoluble and arranges itself into a three dimensional network of meshed strands which entraps red blood cells. The individual strands are approximately 0.2 microns in diameter and the mesh size is approximately 1 micron. Accordingly, five micron red blood cells are easily trapped within the three dimensional "net".
When a thrombus forms, it effectively stops the flow of blood through the zone of formation. If the thrombus extends across the interior diameter of an artery, it cuts off the flow of blood through the artery. If one of the coronary arteries is 100% thrombosed, the flow of blood is stopped in that artery resulting in a shortage of oxygen carrying red blood cells to supply the muscle (myocardium) of the heart wall. Such a thrombosis is unnecessary to prevent loss of blood but can be undesirably triggered within an artery by damage to the arterial wall from atherosclerotic disease. Thus, the underlying disease of atherosclerosis may not cause acute oxygen deficiency (ischemia) but can trigger acute ischemia via induced thrombosis. Similarly, thrombosis of one of the carotid arteries can lead to stroke because of insufficient oxygen supply to vital nerve centers in the cranium. Oxygen deficiency reduces or prohibits muscular activity, can cause chest pain (angina pectoris), and can lead to death of myocardium which permanently disables the heart to some extent. If the myocardial cell death is extensive, the heart will be unable to pump sufficient blood to supply the body's life sustaining needs. The extent of ischemia is affected by many factors, including the existence of collateral blood vessels and flow which can provide the necessary oxygen.
Coronary artery bypass graft (CABG) surgery is a surgical method for bypassing coronary arteries which, because of narrowing or obstruction, are unable to supply adequate oxygen to heart muscle. In recent years, direct administration of chemical lysing agents into the coronary arteries has shown to be of some benefit to patients who have thrombosed coronary arteries. In this procedure, a catheter is placed immediately in front of the blockage and a drip of streptokinase is positioned to be directed at the upstream side of the thrombus. Streptokinase is an enzyme which is able in time to dissolve the fibrin molecule. This procedure can take several hours and is not always successful in breaking up the thrombus. Furthermore, it can lead to downstream thrombus fragments (emboli) which can lead to blockage of smaller diameter branches. It would be useful to have a device and method which would permit essentially instantaneous removal of the blocking thrombus.